Nah that wasn't why they killed her and they weren't even the ones who added X-23 to the book. DeFilippis and Weir were still supposed to be writing post-House of M and mentioned at the time that editorial forced X-23 on them in a "well we kind of had a tough time with her at first but we've hit a groove with her" sort of way. Then out of nowhere and with no warning they got booted off of the book and replaced by Kyle and Yost.
As for why they killed her? No idea really, you'd probably have to ask one of them. I suspect it was because they didn't really care for the New Mutants because they weren't as cool power wise as the Hellions and also for cheap drama for Josh... which then goes into the "cool powers" thing because it caused Elixir to get that black form with the death touch instead of the healing touch.
The real victim of X-23 shilling in that run was Sofia who got depowered and written out of the book so her boyfriend Hellion could start getting shipped with X-23. All of the characters got fucked over hard during that initial story. A bunch of cool or potentially cool characters got depowered and then blown up and then most of the non-Hellion/New Mutant ones that were kept around were never really developed outside of Pixie and Anole; even Loa after she became Elixir's girlfriend got more use in a fucking Namor book than she did in the books that were starring her boyfriend. I'm just glad nobody's put her in their crosshairs because she's cool. Carey seemed to like Trance but her appearances stopped when he left.
Shit even Mercury got fucked because she's now in an out of left field lesbian relationship with the single worst X-Man to ever exist with said relationship only coming around after Bling! stalked her like a creep, got told to fuck off, lied about her being a homophobe, sexually assaulted Jubilee and all of this led to Mercury deciding she should give Bling! a chance even though she'd never been shown to be the slightest bit gay.